(1) Field of the Invention
The present invention generally relates to sensing devices capable of detecting ethyl alcohol (ethanol). More particularly, this invention relates to an ethanol sensor capable of operating passively to determine the level of intoxication of a person in a confined space, such as the passenger compartment of a motor vehicle.
(2) Description of the Related Art
Intoxicated drivers cause about one third of the fatal automobile accidents that occur in the United States. Because any decrease in the frequency or severity of such accidents would be of considerable benefit, various efforts have been undertaken to develop sensors that detect the blood alcohol content (BAC) or, more typically, the breath alcohol content (BrAC), of drivers as an input to vehicle safety systems. U.S. Pat. No. 4,039,852 is representative of one type of sensor, in which the driver is required to blow into a collection tube before the vehicle can be operated. U.S. Pat. No. 5,907,407 is representative of what may be termed a passive sensing system, in which air from the passenger compartment is automatically drawn to a sensing device, such that the driver's natural exhalation is the basis for sensing the driver's BrAC, from which BAC can be determined. Another example of an alcohol sensor in use is a sensor built into a flashlight or clipboard that a police officer can insert into a vehicle passenger compartment to detect the presence of alcohol vapors in the passenger compartment. The alcohol sensing element used is typically based on an electrochemical detection method. The sensing element typically has two electrodes on a proton-conducting solid polymer electrolyte, such as NAFION, a perfluorinated polymer membrane commercially available from E. I. duPont de Nemours and Company. Such sensing elements are described, for example, in U.S. Pat. No. 4,820,386.
In addition to fuel cells, various other types of sensing elements capable of detecting ethanol vapors are known. For example, the above-noted U.S. Pat. No. 5,907,407 utilizes a laser spectroscopy technique to detect the presence of ethanol vapors, while U.S. Pat. No. 4,039,852 makes use of an alcohol-sensitive element whose electrical resistance decreases when subjected to an alcohol-containing atmosphere. Sensing elements of the latter type include those that measure the conductivity of a tin oxide film, which in addition to responding to ethanol vapors also responds to other species, reducing the accuracy of the sensor.
There is an ongoing need for sensors capable of reliably detecting the alcohol impairment of an individual, and particularly for such a sensor capable of use in a passive on-vehicle sensing system to detect the impairment of a driver.